The present invention relates in general to communications systems, and is more particularly directed to a simplex power feeding arrangement for furnishing power from a central location to a remote location in a high-speed data communications system.
This invention is directed towards the reduction of distortion in the signal transfer from the central location to the remote location that may be caused by a flux imbalance in the coupling transformers. This flux imbalance can cause a reduction of the data transmission rates in high-speed communication systems.
Simplex power feeding arrangements, by their nature, cause very little additional net DC flux density in a transformer. Typically, only an imbalance in the ampere-turns product of each half of the line-side transformer windings causes an undesirable additional DC flux density sometimes referred to as a flux imbalance. However, as transformers become smaller and data signal constellations have an increasing number of points, even a slight flux imbalance may cause significant and undesirable distortion in transmission signals. This distortion produces the most negative effect in echo-cancelled systems, where the local transmitter signal must be precisely cancelled to allow error-free reception of the remote signal. Distortion-free coupling of the local signal makes cancellation a relatively simple linear process, as compared to a complex non-linear process that might otherwise be required. Hence, there is a need for a way to counteract the imbalance in the transformer and thereby remove or reduce the distortion or non-linearity.
The problem of distortion caused by the flux imbalance may be solved if there is a way to counteract the magnetomotive force that produces the imbalance. Such a solution could achieve near maximum linearity while maintaining minimum size components.
In order to understand the benefits of a simplex powering apparatus and the flux imbalance problem it is useful to review a data communication system 100 shown in FIG. 1 with a simplex powering arrangement. The data communication system 100 utilizes a line powering supply 105 that may be located at a central location 96 of the communication system 100. This line powering supply 105 transfers power via communication lines 108, 109 to a power supply 106 at a remote location 98. The communication lines 108, 109 are typically twisted pair lines. The power supply 106 at the remote location 98 provides power to remote data communications equipment, such as transceivers 110 and 112, or other data communications devices.
Although variations in the electrical characteristics of each coupling transformer 121, 122, 123, 124 or lines 108, 109 connecting the central location 96 to the remote location 98 are small, slight variations may cause a net DC flux density. This net DC flux density produces distortion in data communication system 100 having small transformers 121, 122, 123, 124. Modulation methods with a large number of constellation points may be affected to a greater extent by the distortion caused by the net DC flux density imbalance. In echo-cancelled systems with a large number of constellation points, the need for linearity is greatest. A highly linear system affords a relatively easy linear cancellation of the near-end signal, as opposed to a relatively difficult non-linear cancellation. Although a larger transformer may reduce the distortion problem, continual market pressure exists to make electronic communication devices smaller while increasing the data rate and therefore the need for constellations with a large number of points. Hence, there is a need for a method of removing the flux imbalance and allowing for the use of smaller sized magnetic devices such as transformers while maintaining or improving performance caused by the distortion due to flux imbalance.